The Cookie Session plugin enables grails applications to store session data in http cookies between requests instead of in memory on the server. This allows application deployments to be more stateless which supports simplified scaling architectures and fault tolerance. Read more

It is mostly useful for logging your REST traffic. Full HTTP web pages can be huge to log and generally waste your space.
I suggest to map all of your REST controllers with the same path in UrlMappings, e.g. `/rest/` and configure this plugin with this path. Read more